The 2-PHASE.TM. (a trademark of the Xerox Corporation) extraction process provides a method and apparatus for removing chemicals and other undesirable substances from a contaminated area of the ground. Generally speaking, an extraction well or the like is placed within the affected area and a vacuum is applied to draw soil vapors and groundwater into the well. Application of the vacuum to the soil vapor initiates a high velocity vapor stream at the bottom of the well, entraining the contaminated groundwater and soil gas. Both phases are then lifted to the surface as a single two-phase stream. The liquid and vapor are then separated, and each phase is treated to remove contaminants. Such processes are disclosed in U.S. Pat. No. 5,464,309 (Mancini 309), U.S. Pat. No. 5,441,365 (Duffney), U.S. Pat. No. 5,358,357 (Mancini 357), U.S. Pat. No. 5,197,541 (Hess 541), U.S. Pat. No. 5,172,764 (Hajali), and U.S. Pat. No. 5,050,676 (Hess 676), all assigned to Xerox Corporation, Stamford, Conn.
Contaminants can be found in subsurface soil and groundwater, in the liquid or vapor phase. They can exist as discrete substances, or they can be mixed with and/or dissolved in groundwater and soil vapors. Such contaminants can be found in the vadose zone (the unsaturated layer that lies between the surface of the earth and the water table), at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
Many industrial and commercial facilities and waste handling and disposal sites contain both soil and groundwater contamination. A variety of techniques have been used for removal of contaminants and remediation of affected media. One common technique entails the excavation and off-site treatment of the soil. Another technique entails saturating the contaminated soil with water in situ, causing the contaminants to be leached slowly from the soil by the water. The contaminated water can then be removed.
One very effective technique for removing chemicals from a contaminated area of the ground involves removal of soil contaminants using the 2-PHASE.TM. extraction process. The process generally involves providing a borehole in the contaminated area, placing an extraction well inside of the borehole, and applying a vacuum to the well such that vapors and liquid can be drawn from the soil. The liquid and vapor are transported to the surface simultaneously as a two-phase stream. After it reaches the surface, the liquid-vapor stream is separated into two independent streams. Each stream is then treated for removal of the contaminants.
Various types of contaminants may be removed from the ground using a process such as two phase extraction. An effluent stream may include organic and inorganic substances, as well as those that are soluble, insoluble, volatile, and non-volatile. The various classes of contaminants are subjected to post-extraction treatment to remove them from the vapor or liquid in which they reside. Suitable post-extraction treatment processes for contaminant removal typically, but not necessarily include filtration, adsorption, air stripping, settling, flocculation, precipitation, scrubbing and the like.
The process described above is a very effective technique for removing volatile and water soluble chemicals from a contaminated area of the ground. However, during the normal course of operation events often occur which alter the height of the water table, and adversely affect operation of the well. For example, as seasonal changes occur the amount of groundwater present in a given area will often vary as snow melts, or excessive heat causes the ground to dry.
Since the volume of contaminated effluent extracted from sub-surface soil varies with the groundwater content, the ratio of entrainment air to groundwater must be manipulated manually or the vacuum being applied to the effluent stream will not lift it from the ground. More specifically, when excess groundwater is present, the anti-gravitational force being applied by the vacuum may be too low to lift the effluent from beneath the ground. Similarly, when the ground is dry the excess soil gas results in greater air flow within the extraction well. The increase in the flow of air causes the vacuum to fluctuate which makes well operation inefficient.
Generally speaking, it is best to keep the bottom of the extraction well at or very near the liquid-vapor interface in order to continuously entrain the suspended liquid within the extracted air stream. The 2-PHASE.TM. process is most efficient when the ratio of vapor to liquid maximizes the vacuum that is applied to the extraction well. Fluctuations in groundwater levels and changes in groundwater flow to the well cause this ratio to vary throughout well operation. This variation in the vapor to liquid ratio requires the flow of entrainment air to be continuously adjusted in order to maintain application of the optimum vacuum to the extraction well. For example, if the liquid-vapor interface drops below the bottom of the well, the amount of air being supplied to the well must be decreased to maintain the vacuum condition. Once groundwater levels rise, the air supply must be increased to optimize the vacuum or the extraction well will again operate inefficiently.
Thus, entrainment air must be adjusted as the groundwater level fluctuates if optimal vacuum delivery to the well formation is to be maintained, and efficient operation of the extraction well is to continue. The vacuum within the well is maintained by supplying atmospheric air through an inlet as the level of groundwater increases. As the groundwater level drops, the air supply is cut-off. The current method of operation requires a technician or other maintenance person to physically travel out to the well site, and inspect the hardware to see if the well is operating properly. If the liquid is no longer being entrained, the technician must manually supply a gas fluid to the well to restart it. While compressed air is often supplied, any suitable gas including those at or below atmospheric pressure and those at above or below ambient temperature may be provided. The inlet must then be manually adjusted to vary the flow of gas therethrough (the air) once the well begins to operate. Because a failure will not be detected until a physical inspection of the hardware is performed, the well may be inoperable for extensive periods of time. It is desirable to provide a way to automatically direct and regulate the amount of air that is applied to the well and extraction tube, as changes to the surrounding groundwater level take place. The present invention provides such means, thereby eliminating the need for human intervention and the costs and inconvenience associated with it.
The following disclosures may be relevant to various aspects of the present invention:
U.S. Pat. No. 5,464,309 to Mancini et al. issued Nov. 7, 1995 discloses certain aspects of the 2-PHASE.TM. extraction process for removing volatile organic chemicals from a contaminated area of the ground. A borehole is placed in the contaminated area to a depth below the water table, and a plurality of concentric pipes are placed in the borehole. Gas and a vacuum are simultaneously applied to the pipe system such that contaminated vapors and liquid are drawn from the soil into the pipes. The vapors and liquids are transported to the surface together and separated into two components. Each stream is treated to remove the contaminants. An apparatus for carrying out the process is also disclosed.
U.S. Pat. No. 5,373,897 to Skarvan issued Dec. 20, 1994 discloses a pneumatic underground fluid recovery pump that includes a power actuated inlet valve and a power source, independent of the static fluid pressure head in the well, for actuating the power actuated inlet valve between open and closed positions. Also disclosed is a pneumatic underground fluid recovery pump that includes a fluid level sensor for sensing fluid level in the pump reservoir above a first predetermined level and a controller for controlling the pressurization of the pump in response to the fluid level sensor sensing fluid level above the first predetermined level. Also disclosed is a pneumatic underground fluid recovery pump that includes a fluid level tracking device for sensing underground fluid level in the well and adjusting the level of the pump inlet valve a predetermined distance below the underground fluid level in the well.
U.S. Pat. No. 5,358,357 to Mancini et al. issued Oct. 25, 1994 discloses a process for removing contaminants from a contaminated area of the ground having a vadose zone and a water table, which comprises providing a borehole in the contaminated area to a depth below the water table; placing in the borehole to a depth below the water table a perforated riser pipe inside of which is situated a vacuum extraction pipe with a bottom opening situated within the perforated riser pipe, said vacuum extraction pipe containing groundwater prior to application of a vacuum thereto, said vacuum extraction pipe having at least one gas inlet situated below the groundwater level in the vacuum extraction pipe; while introducing a gas into the riser pipe, applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a two-phase common stream; introducing a gas into the vacuum extraction pipe at a level below the groundwater level in the vacuum extraction pipe to initiate two-phase flow within the vacuum extraction pipe; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and separately treating the separated liquid and gas streams.
U.S. Pat. No. 5,172,764 to Hajali et al. issued Dec. 22, 1992 discloses a process for removing contaminants from a contaminated area of the ground having a vadose zone and a water table which comprises providing a borehole in the contaminated area; placing in the borehole a perforated riser pipe inside of which is situated a vacuum extraction pipe with an opening situated near, at, or at any point below the water table within the perforated riser pipe; while introducing a gas into the riser pipe, applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a common stream; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and separately treating the separated liquid and gas streams. Also disclosed is an apparatus for carrying out the process.
U.S. Pat. No. 5,147,530 to Chandler et al. issued Sep. 15, 1992 discloses a well water removal and treatment system including a pumping and well water withdrawal loop consisting of an above ground pump, a pressurized water drive line from the pump outlet to a well water ejector, a water return line from the well water ejector to an aeration and precipitation tank, an inlet line from the aeration and precipitation tank to the pump and a venturi nozzle air mixing manifold fluidically connected between the high pressure drive water line and the lower pressure water delivery line to mix air into the water during the entire pump cycle. The water delivery line from the pumping and withdrawal loop has a flow control regulator therein that controls the water flow therethrough in proportion to the water pressure in the pumping and withdrawal loop above a preselected minimum control level. Until the water pressure exceeds the minimum control level, the water repeatedly cycles through the pumping and withdrawal loop and thereafter most of the water repeatedly cycles through the loop until the pump is deactuated.
U.S. Pat. No. 4,844,797 to Wells issued Jul. 4, 1989 discloses a vacuum extraction system in which one or more vacuum extraction vessels are suspended in one or more well bores and each is connected to a vacuum pump. In one embodiment, each extraction vessel has a vessel chamber, a top inlet port with an adjustable metering valve, a vent pipe, a liquid level sensor in the vessel chamber, and an outlet port connected to the vacuum pump through a controller. The controller responds to the level of liquid in the vessel chamber to connect and disconnect each of the outlet ports of each of the extraction vessels to and from the vacuum pump. The controller also activates and deactivates the vacuum pump. In another embodiment, the extraction vessel is suspended for reciprocation in the well bore in order to skim liquid hydrocarbons floating on the ground water. In another embodiment, the extraction vessel has a differentiation valve in its bottom which releases water, but not liquid hydrocarbons, when the extraction vessel is lifted free of the liquid in the well.
U.S. application Ser. No 08/919,966 filed Aug. 28, 1997 by Salotti et al. as a continuation of application Ser. No. 08/606,785 filed Feb. 27, 1995 discloses an air flow control circuit which includes a conduit having a first end and a second end, each end defining an aperture through which air may pass. The first end of the conduit is located inside an inner wall of a riser pipe, and outside an outer wall of a vacuum extraction pipe such that air may move from the conduit into the vacuum extraction pipe. A check valve assembly is situated in the conduit between an inlet to the riser pipe and an opening in the vacuum extraction pipe.
All of the references cited herein are incorporated by reference for their teachings.
Accordingly, although known apparatus and processes are suitable for their intended purposes, a need remains for processes and apparatus for pre-treating contaminated liquids and gases obtained from soil with increased efficiency. Further, there is a need for processes and apparatus for enhancing the concentration of volatile contaminants in the gas phase of an effluent mixture, thereby decreasing the concentration of contaminants in the liquid phase.